Ni Xiang, Weiner Matthew, Alù Andrea, Khanikaev Alexander B
Department of Electrical Engineering, Grove School of Engineering, City College of the City University of New York, New York, NY, USA.
Physics Program, Graduate Center of the City University of New York, New York, NY, USA.
Nat Mater. 2019 Feb;18(2):113-120. doi: 10.1038/s41563-018-0252-9. Epub 2018 Dec 31.
Topological systems are inherently robust to disorder and continuous perturbations, resulting in dissipation-free edge transport of electrons in quantum solids, or reflectionless guiding of photons and phonons in classical wave systems characterized by topological invariants. Recently, a new class of topological materials characterized by bulk polarization has been introduced, and was shown to host higher-order topological corner states. Here, we demonstrate theoretically and experimentally that 3D-printed two-dimensional acoustic meta-structures can possess nontrivial bulk topological polarization and host one-dimensional edge and Wannier-type second-order zero-dimensional corner states with unique acoustic properties. We observe second-order topological states protected by a generalized chiral symmetry of the meta-structure, which are localized at the corners and are pinned to 'zero energy'. Interestingly, unlike the 'zero energy' states protected by conventional chiral symmetry, the generalized chiral symmetry of our three-atom sublattice enables their spectral overlap with the continuum of bulk states without leakage. Our findings offer possibilities for advanced control of the propagation and manipulation of sound, including within the radiative continuum.
拓扑系统本质上对无序和连续扰动具有鲁棒性，这导致了量子固体中电子的无耗散边缘输运，或者在以拓扑不变量为特征的经典波系统中光子和声子的无反射引导。最近，一类以体极化特征的新型拓扑材料被引入，并被证明拥有高阶拓扑角态。在此，我们通过理论和实验证明，3D打印的二维声学超结构可以具有非平凡的体拓扑极化，并拥有具有独特声学特性的一维边缘态和Wannier型二阶零维角态。我们观察到由超结构的广义手性对称性保护的二阶拓扑态，这些态局域在角上并被钉扎到“零能量”。有趣的是，与由传统手性对称性保护的“零能量”态不同，我们三原子子晶格的广义手性对称性使它们的能谱与体态连续区重叠而无泄漏。我们的发现为声音的传播和操控的先进控制提供了可能性，包括在辐射连续区内。
